Mean-Field Bounds and the Classical Nature of Thermal Conduction in Nanofluids

2008 ◽  
Author(s):  
Jacob Eapen
Keyword(s):  
Thermal Conductivity ◽  
Thermal Conduction ◽  
Conduction Mechanism ◽  
Linear Chain ◽  
Mean Field ◽  
Liquid Mixtures ◽  
Large Set ◽  
Inhomogeneous Systems ◽  
Conduction Behavior ◽  
Intermediate Configuration

The initial promise of nanofluids as an advanced, nanoengineered coolant has been tempered in the recent years by a conspicuous lack of consensus on its thermal conduction mechanism. Several new mechanisms have been hypothesized in the recent years to characterize the thermal conduction behavior in nanofluids. In this presentation, we show that a large set of nanofluid thermal conductivity data is enveloped by the well-known Hashin and Shtrikman (H-S) mean-field bounds for inhomogeneous systems. The thermal conductivity in nanofluids, therefore, is largely dependent on whether the nanoparticles stays dispersed in the base fluid, form linear chain-like configurations, or assume an intermediate configuration. The experimental data, which is strikingly analogous to those in most solid composites and liquid mixtures, provides a strong evidence for the classical nature of thermal conduction in nanofluids.

scholarly journals The Classical Nature of Thermal Conduction in Nanofluids

2010 ◽  
Vol 132 (10) ◽  
Author(s):  
Jacob Eapen ◽  
Roberto Rusconi ◽  
Roberto Piazza ◽  
Sidney Yip
Keyword(s):  
Experimental Data ◽  
Thermal Conductivity ◽  
Strong Evidence ◽  
Thermal Conduction ◽  
Base Fluid ◽  
Liquid Mixtures ◽  
Large Set ◽  
Conductivity Data ◽  
Homogeneous Systems ◽  
Thermal Conductivity Data

We show that a large set of nanofluid thermal conductivity data falls within the upper and lower Maxwell bounds for homogeneous systems. This indicates that the thermal conductivity of nanofluids is largely dependent on whether the nanoparticles stay dispersed in the base fluid, form large aggregates, or assume a percolating fractal configuration. The experimental data, which are strikingly analogous to those in most solid composites and liquid mixtures, provide strong evidence for the classical nature of thermal conduction in nanofluids.

The Effect of Point Defects Induced by Fast Neutron Irradiation on the Thermal Conductivity of Boron Carbide

2017 ◽  
Vol 726 ◽  
pp. 153-158
Author(s):  
Ai Bing Du ◽  
Zhi Xue Qu ◽  
Xi Ping Su ◽  
Xiao Xiao
Keyword(s):  
Thermal Conductivity ◽  
Boron Carbide ◽  
Temperature Dependence ◽  
Fast Neutron ◽  
Point Defects ◽  
Thermal Conduction ◽  
Conduction Model ◽  
Initial Stage ◽  
Fast Neutron Irradiation ◽  
Conduction Behavior

The thermal conduction behavior of the neutron absorbing ceramic boron carbide in the initial stage of the irradiation was analyzed and a classical thermal conduction model was used to estimate the variation of the thermal conductivity in this paper. The calculated thermal conductivity using the model shows a large degration in the initial stage of irradiation. As the burnup increases, the thermal conductivity turns to be free of temperature dependence. These calculated results are consistent well with the expermental data of thermal conductivity of the irradiated boron carbide, which may suggest that the variation of the thermal conductivity of boron carbide is predominantly determined by the point defects scattering in the initial stage of irradiation.

Thermal Conduction Mechanism in Nanofluids, Solid Composites and Liquid Mixtures

2009 ◽  
Author(s):  
Jacob Eapen
Keyword(s):  
Thermal Conductivity ◽  
Lower Bound ◽  
Effective Medium Theory ◽  
Mean Field ◽  
Liquid Mixtures ◽  
Conduction Path ◽  
Medium Theory ◽  
Base Medium ◽  
Dispersed Medium ◽  
Solid Composites

Analysis of Maxwell’s mean-field (or effective-medium) theory reveals two limiting bounds — an upper and a lower bound — for thermal conductivity in binary composite systems. The lower and the upper bounds correspond to continuous conduction paths through the base medium and the dispersed medium, respectively (assuming that the dispersed medium has a higher thermal conductivity). Extensive comparisons to experimental data show that most of the reported thermal conductivity data on nanofluids, solid composites and liquid mixtures fall between the limiting Maxwell bounds. For a nanofluid, this indicates that the effective thermal conductivity is largely dependent on the geometrical configuration and the connectivity of the dispersed nanoparticle phase. The lower bound corresponds to a colloidal configuration of well-dispersed nanoparticles with the continuous conduction path provided by the base medium while the upper bound represents a linear, fractal-like nanoparticle arrangement with the continuous conduction path provided by the nanoparticles.

Transition temperature and thermal conduction behavior of slag in gasification process

Energy ◽  
2021 ◽  
Vol 222 ◽  
pp. 119940
Author(s):  
Qiang Li ◽  
Qian Wang ◽  
Jiansheng Zhang ◽  
Weiliang Wang ◽  
Jizhen Liu
Keyword(s):  
Transition Temperature ◽  
Thermal Conduction ◽  
Gasification Process ◽  
Conduction Behavior

Influence of the Material and Thickness of the Specimen on an Infrared Stress Image

2004 ◽  
Vol 261-263 ◽  
pp. 1641-1646
Author(s):  
Kenji Machida ◽  
Mamtimin Gheni
Keyword(s):  
Thermal Conductivity ◽  
Hybrid Method ◽  
Thermal Conduction ◽  
Crack Problem ◽  
High Stress ◽  
High Accuracy ◽  
Problem Analysis ◽  
Principal Stresses ◽  
Distribution Form ◽  
Stress Components

The thickness dependency of the temperature image obtained by an infrared thermography was investigated using specimens with three kinds of materials and four kinds of the thickness of the specimen. Only the sum of the principal stresses which is the first invariant of stress tensor is measured, and it is impossible to measure individual stress components directly. Then, the infrared hybrid method was developed to separate individual stress components. Although the form of the contour line of low stress side differs greatly, the distribution form of high stress side was considerably alike. The stress intensity factor of material with low thermal conductivity can be estimated with high accuracy by the infrared hybrid method. On the crack problem, it was elucidated that the influence of thermal conduction is large and an inverse problem analysis is required.

ABSENCE OF PHASE TRANSITIONS ON TREE STRUCTURES

1993 ◽  
Vol 07 (29n30) ◽  
pp. 1947-1950 ◽  
Author(s):  
RAFFAELLA BURIONI ◽  
DAVIDE CASSI
Keyword(s):  
Long Range ◽  
Nearest Neighbor ◽  
Linear Chain ◽  
Mean Field ◽  
Range Order ◽  
The Other ◽  
Long Range Order ◽  
Field Phase ◽  
Tree Structures ◽  
Bethe Lattices

We rigorously prove that the correlation functions of any statistical model having a compact transitive symmetry group and nearest-neighbor interactions on any tree structure are equal to the corresponding ones on a linear chain. The exponential decay of the latter implies the absence of long-range order on any tree. On the other hand, for trees with exponential growth such as Bethe lattices, one can show the existence of a particular kind of mean field phase transition without long-range order.

Thermal conduction characteristics of silicone composites including ultrasonic-treated graphite

2021 ◽  
pp. 002199832110595
Author(s):  
Weontae Oh ◽  
Jong-Seong Bae ◽  
Hyoung-Seok Moon
Keyword(s):  
Thermal Conductivity ◽  
Ultrasonic Treatment ◽  
Thermal Conduction ◽  
Light Emitting Diode ◽  
Thermal Interface Material ◽  
Ultrasonic Power ◽  
Lighting System ◽  
Thermal Interface ◽  
Light Emitting ◽  
Inorganic Oxides

The microstructural change of graphite was studied after ultrasonic treatment of the graphite. When the graphite solution was treated with varying ultrasonic power and time, the microstructure changed gradually, and accordingly, the thermal conductivity characteristics of the composite containing the as-treated graphite was also different with each other. Thermal conductivity showed the best result in the silicone composite containing graphite prepared under the optimum condition of ultrasonic treatment, and the thermal conductivity of the composite improved proportionally along with the particle size of graphite. When the silicone composite was prepared by using a mixture of inorganic oxides and graphite rather than graphite alone, the thermal conductivity of the silicone composite was further increased. A silicone composite containing graphite was used for LED (light emitting diode) lighting system as a thermal interface material (TIM), and the temperature elevation due to heat generated, while the lighting was actually operated, was analyzed.

scholarly journals Design and Implementation of a Laboratory Equipment for Studying Heat Transfer by Conduction

2019 ◽  
Vol 11 (1) ◽  
pp. 153-156
Author(s):  
István Padrah ◽  
Judit Pásztor ◽  
Rudolf Farmos
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Conduction ◽  
Thermal Conduction ◽  
Transfer Mechanism ◽  
Measuring Instrument ◽  
Heat Transfer Mechanism ◽  
Laboratory Equipment ◽  
Insulating Materials ◽  
Design And Implementation

Abstract Thermal conduction is a heat transfer mechanism. It is present in our everyday lives. Studying thermal conductivity helps us better understand the phenomenon of heat conduction. The goal of this paper is to measure the thermal conductivity of various materials and compare results with the values provided by the manufacturers. To achieve this we assembled a measuring instrument and performed measurements on heat insulating materials.

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